Biliary and pancreatic cancers often are diagnosed when the patient presents specific symptoms characteristic of a blockage of either the patient's bile and/or pancreatic duct. In the case of a biliary cancer, the symptoms often include jaundice. Unfortunately, by the time such a stage of either disease is reached, the tumor is usually at an advanced stage and, therefore, is inoperable. Accordingly, management of the disease at this stage usually consists of palliation only.
Although surgical bypass procedures can be effective for palliation, most patients presenting with biliary or pancreatic cancer are either too sick to undergo major bypass surgery or have too short a remaining life-span to make such duct bypass surgery advisable. Therefore, palliation of jaundice or other symptoms associated with biliary or pancreatic cancer is most often accomplished using an endoscopically inserted stent or endoprosthesis that is positioned to bridge the obstructed area, i.e., so as to maintain a fluid flow pathway across (or past) the obstruction.
The prior art includes several examples of stents that have been and continue to be employed during endoscopic procedures so that flow of biological fluids may be reasserted in a patient. Generally, there are two types of stents that are typically employed: 1) plastic and 2) metal. Conventional plastic stents, formed in the shape of a cylinder, have a tendency to clog with debris and form a biofilm early in their use, which means that these stents have a limited operational lifetime. Conventional metal stents provide an improved operational lifetime over plastic stents because they are designed with a larger initial lumen. However, metal stents are often many times more expensive than plastic stents. In addition, since metal stents, like their plastic counterparts, are tubular in design, they also have a tendency to clog during their operational lifetimes. Moreover, metal stents are technically more difficult to insert into the patient and, once in place, cannot be removed.
Specific designs for stents and drains are known in the art. Several examples of known stents and drains are discussed below.
U.S. Pat. Nos. 5,486,191 and 5,776,160 both describe a winged biliary stent that has a central wire stylet lumen 18 surrounded by a core and several, grooved wings 14. Each wing 14 has a width that is substantially larger than the width of the core. The wings 14 may be disposed around the core in a helical fashion, if desired. Rather than discharge biological flow through a lumen through the center of the device, these stents permit flow across the exterior surfaces of the grooved wings 14.
French Patent No. 564,832 illustrates a surgical drain. The surgical drain has a large opening that passes through its center. The surface of the drain includes helically-disposed surface protrusions.
German Patent No. 88138 illustrates a wound drain that has a plus-shaped cross-section. It appears that there is a small hole passing through the longitudinal center of the device. Moreover, it also appears that there are a number of semicircular holes passing laterally through the four radial extensions. One end of the drain includes a protrusion, labeled “d.”
British Patent No. 105,038 also describes a surgical drain with a plus-shaped cross-section. As the patent describes, by allowing the patient's tissue to form the walls of the drain, the tissue's normal undulations assist in the drainage of fluid from the wound. One embodiment of the drain described includes three arms extending outwardly from a central core through which is provided a central opening or passage.
European Patent No. 0 059 620 describes a wound drain catheter with a plurality of strut portions 32 capped with overhang portions 34. The drain is designed to be inserted into a wound and to be connected to a vacuum source to pull fluids from the wound.
U.S. Pat. No. 4,307,723 describes a urethral stent 10 with a central lumen 23 and several grooves 17 in the stent 10. The stent 10 includes hooked ends 13, 14, which are commonly referred to as “pig tails” in the stent art. Pig tails help hold the stent in position, after the stent has been placed within the patient.
British Patent No. 189,127 describes a wound drainage plug with a central duct E from which several ribs B extend. The ribs B form triangular grooves A around the periphery of the wound drain. The drain preferably is made of India rubber.
Soviet Patent No. 1641356 appears to illustrate a drain with a plurality of ribs extending outwardly from a central portion. The ribs appear to be helically disposed around the drain.
U.S. Pat. No. 6,132,471 describes a stent for draining the pancreatic and biliary ducts. The stent 20 is made from a soft, biocompatible material. The stent is tubular in shape with a smooth, continuous outer surface and an internal lumen 25, 45. The distal end portion 30 of the stent 20 is formed into a conical or tapered shape 40. The proximal end 35 of the stent 20 does not include a tapered section 40.
U.S. Patent Application Publication No. 2001/0041929 describes a stent 1 that is designed for placement in narrow portions of hollow vessels within the human body. The stent is essentially a cylindrical body with a central channel permitting fluid to pass therethrough. The stent body 2 is made of a flexible web material, even though it is illustrated as a solid, cylindrical tube. The first and second end portions 3, 4 have wall thicknesses WE1 and WE2 that are smaller than the wall thickness WH of the central portion 5. As the patent discusses, the differing wall thicknesses alter the flexibility of the stent 1 by comparison with a stent that does not include this feature.
U.S. Patent Application Publication No. 2003/0100859 describes an arterio-venous shunt graft 10. The shunt graft 10 has a main body 12 with an arterial end 14 and a venous end 16. The main body 12 may have a tapered portion 20 adjacent to the arterial end 14. A plurality of ribs 22 are formed on the exterior of the main body 12.
U.S. Pat. No. 6,124,523 describes an encapsulated stent 200 that is radially expandable. The stent 200 has a central passage or lumen 28 passing therethrough. The stent 200 includes opposing ends 216, 218 that flare radially outwardly after the stent is radially enlarged. Barbs 213 are formed on the second tubular member 214 (the outer member) to assist in fixation of the device, once expanded.
While adequate for the medical procedures described in each of the references discussed above, the prior art fails to provide a design for a stent that is simple to manufacture, may be easily inserted into the biliary or pancreatic tract of a patient, and includes one or more securement features so that it resists the tendency to migrate within the patient, even if emplaced within the patient for an extended period of time.